Substrate processing method and substrate processing apparatus

ABSTRACT

In a substrate processing apparatus, a control electrode ( 131 ) separates a process space ( 11 C) including a substrate to be processed and a plasma formation space ( 11 B) not including the substrate. The control electrode includes a conductive member formed in a processing vessel and having a plurality of apertures ( 131   a ) for passing plasma. A surface of the control electrode is covered by an aluminum oxide or a conductive nitride. In the substrate processing apparatus, a gas containing He and N 2  is supplied into the processing vessel. In the plasma formation space, there is formed plasma under a condition in which atomic state nitrogen N* are excited. The atomic state nitrogen N* are used to nitride a surface of the substrate.

TECHNICAL FIELD

The present invention generally relates to plasma processing apparatusesand more particularly to a microwave plasma processing apparatus.

Plasma process and plasma processing apparatus constitute indispensabletechnology for fabricating ultrafine semiconductor devices such as theone called deep submicron device or deep sub-quarter micron devicehaving a gate length near 0.1 μm or less, or for fabricatinghigh-resolution flat panel display device including a liquid crystaldisplay device.

Conventionally, various plasma excitation methods have been employed inthe plasma processing apparatus used for fabricating semiconductordevices or liquid crystal display devices. Particularly, high-frequencyplasma apparatuses of parallel plate type or induction-coupled typeplasma apparatus are used commonly. However, such a conventional plasmaprocessing apparatuses suffers from the problem of non-uniform plasmaformation in that the region in which high electron density is achievedis substantially limited, and there has been a difficulty in conductinga uniform processing over the entire surface of the substrate with alarge processing rate or throughput. This problem becomes particularlyserious in the case of processing a substrate of large diameter.Further, such a conventional plasma processing apparatus has inherentproblems, associated with its high electron temperature, in that damagesare caused in the semiconductor devices formed on the substrate.Further, severe metal contamination may be caused as a result ofsputtering of the chamber wall. Thus, it is becoming difficult withconventional plasma processing apparatuses to satisfy the stringentdemand of further miniaturization and further improvement ofproductivity of semiconductor devices or flat display devices.

Meanwhile, there has been a proposal of a microwave plasma processingapparatus that uses high-density plasma excited, not by d.c. magneticfield, but by a microwave electric field. For example, there is aproposal of a plasma processing apparatus that excites plasma byemitting a microwave into a processing vessel from a planar antenna(radial line slot antenna) having a number of slots arranged so as toproduce a uniform microwave, for emitting a microwave into a processingvessel. In this plasma processing apparatus, the microwave electricfield induces plasma by causing ionization in the gas in the vacuumvessel. Reference should be made to Japanese Laid-Open PatentApplication 9-63793. By using the microwave plasma excited according tosuch a process, it becomes possible to realize a high-plasma densityover a wide area right underneath the antenna, and uniform plasmaprocessing becomes possible with short time period. Further, themicrowave plasma thus excited has an advantageous feature of lowelectron temperature as a result of excitation of the plasma by using amicrowave, and it becomes possible to avoid the problem of damages ormetal contamination caused in the substrate. Further, it becomespossible to excite uniform plasma over a substrate of large area, andthus, the plasma processing apparatus can easily handle the fabricationof semiconductor devices on a large-diameter semiconductor wafer orfabrication of large flat panel display devices.

BACKGROUND ART

FIG. 1 shows the schematic construction of a conventionalinduction-coupled plasma processing apparatus 1.

Referring to FIG. 1, the plasma processing apparatus 1 includes aprocessing vessel 2 of a quartz dome evacuated by an evacuation line 2A,and there is provided a stage 3 in a process space 2B defined by theprocessing vessel 2 such that the stage 2 is rotated by a rotatingmechanism 3A. Further, a substrate 4 is held on the stage 3. Further, aninert gas such as Ar and a process gas such as oxygen or nitrogen aresupplied to the process space 2B via a process gas supply line 2C.Further, there is provided a coil 5 around the top part of theprocessing vessel 2 at the outside thereof, and high-density plasma 2Dis inducted at the top part of the process space 2B by driving the coil5 by a d.c. power source.

In the plasma processing apparatus 1 of FIG. 1, the radicals of theprocess gas formed with the high-density plasma 2D reach the surface ofthe substrate 4 and the substrate processing such as oxidation ornitridation is achieved.

In such a conventional induction-coupled plasma processing apparatus 1,on the other hand, there exists a drawback in that the high-densityplasma 2D is localized at the top part of the processing vessel andthere appears an extremely non-uniform distribution in the radicals thatare formed with the plasma. Particularly, the non-uniformity of theradical concentration in the radial direction of the substrate is notresolved even when the stage 3 is rotated by the rotating mechanism 3A.

Thus, in the conventional induction-coupled plasma processing apparatus1, the plasma processing apparatus was designed such that the substrate4 is separated from the region in which the high-density plasma 2D isformed with a large distance for realizing as uniform radicalconcentration distribution as possible at the surface of the substrate4. As a result of such a construction, on the other hand, the overallsize of the substrate processing apparatus 1 is increased inevitably.Further, the amount of the radicals reaching the substrate 4 is reduced.These problems become particularly serious in the technology of currenttrend of processing a large-diameter substrate.

On the other hand, there is a proposal of a microwave plasma processingapparatus that uses high-density plasma induced, not by an inductionmagnetic field but by a microwave electric field. For example, there isproposed a plasma processing apparatus that uses a planar antenna(radial line slot antenna) having a large number of slots arranged so asto produce a uniform microwave, for emitting a microwave into aprocessing vessel. In this apparatus, the microwave electric field thusinduced is used to excite plasma by causing ionization in the gas in thevacuum vessel. Reference should be made to Japanese Laid-Open PatentApplication 9-63793. By using the microwave plasma excited according tosuch a process, it becomes possible to realize a high-plasma densityover a wide area right underneath the antenna, and uniform plasmaprocessing becomes possible with short time period. Further, themicrowave plasma thus excited has an advantageous feature of lowelectron temperature as a result of excitation of the plasma by using amicrowave, and it becomes possible to avoid the problem of damages ormetal contamination caused in the substrate. Further, it becomespossible to excite uniform plasma over a substrate of large area, andthus, the plasma processing apparatus can easily handle the fabricationof semiconductor devices on a large-diameter semiconductor wafer orfabrication of large flat panel display devices.

FIG. 2 shows the construction of a microwave plasma processing apparatus10 that uses such a radial line slot antenna as proposed before by theinventor of the present invention.

Referring to FIG. 2, the microwave plasma processing apparatus 10includes a processing chamber 11 evacuated at a plurality of evacuationports 11 a, and there is provided a stage 13 inside the processingchamber 11 for supporting a substrate 12 to be processed. In order toachieve uniform evacuation of the processing chamber 11, there isprovided a ring-shaped space 11A around the stage 13, and the processingchamber 11 is evacuated uniformly via the space 11A and further via theevacuation ports 11 a by arranging the evacuation ports 11 acommunicating with the space 11A in axial symmetry with respect to thesubstrate.

On the processing chamber 11, there is provided a plate-like showerplate 14 formed of a low-loss dielectric such as Al₂O₃ or SiO₂ as a partof the outer wall of the processing chamber 11 at a location facing thesubstrate 12 held on the stage 13, wherein the shower plate 14 isprovided via a seal ring not illustrated and includes a number ofapertures 14A. Further, a cover plate 15 also of a low-loss dielectricsuch as Al₂O₃ or SiO₂ is provided at the outer side of the shower plate14 via another seal ring not illustrated.

The shower plate 14 is provided with a gas passage 14B at a top surfacethereof, and each of the apertures 14A are provided so as to communicatewith the gas passage 14B. Further, there is provided a gas supplypassage 14C in the interior of the shower plate 14 in communication witha gas supply port lip provided at an outer wall of the processing vessel11. Thus, the plasma-excitation gas such as Ar or Kr supplied to the gassupply port 11 p is forwarded to the apertures 11A via the supplypassage 14C and further via the passage 14B and is released to theprocess space 11B right underneath the shower plate 14 inside theprocessing vessel 11 from the foregoing apertures 14A.

On the processing vessel 11, there is further provided a radial lineslot antenna 20 at the outer side of the cover plate 15 with aseparation of 4-5 mm from the cover plate 15. The radial line slotantenna 20 is connected to an external microwave source (notillustrated) via a coaxial waveguide 21 and causes excitation of theplasma-excitation gas released into the process space 11B by themicrowave from the microwave source. It should be noted that the coverplate 15 and the radiation surface of the radial line slot antenna arecontacted closely, and there is provided a cooling block 19 on theantenna 20 for cooling the antenna. The cooling block 19 includes acooling water passage 19A.

The radial line slot antenna 20 is formed of a flat, disk-shaped antennabody 17 connected to an outer waveguide tube 21A of the coaxialwaveguide 21 and a radiation plate 16 provided at the opening of theantenna body 17, wherein the radiation plate 16 is formed with a numberof slots and a retardation plate of a dielectric plate having a constantthickness is interposed between the antenna body 17 and the radiationplate 16.

In the radial line slot antenna 20 having such a construction, themicrowave fed thereto from the coaxial waveguide 21 propagates along apath between the disk-shaped antenna body 17 and the radiation plate 16in the radial direction, wherein the microwave thus propagatingundergoes compression of wavelength as a result of the existence of theretardation plate 18. Thus, by forming the slots concentrically incorrespondence to the wavelength of the microwave thus propagating inthe radial direction, and by forming the slots so as to form aperpendicular angle with each other, it becomes possible to emit a planewave having a circular polarization from the radial line slot antenna 20in the direction substantially perpendicular to the radiation plate 16.

By using such a radial line slot antenna 20, there is formed uniformhigh-density plasma in the process space 11B right underneath the showerplate 14. The high-density plasma thus formed has a feature of lowelectron temperature and the occurrence of damages in the substrate 12to be processed is avoided. Further, there occurs no metal contaminationcaused by sputtering of the chamber wall of the processing vessel 11.

Thus, by supplying a process gas, such as an O₂ gas, an NH₃ gas, or amixed gas of an N₂ gas and an H₂ gas, to the gas inlet port 11 p of thesubstrate processing apparatus 10 of FIG. 2 in addition to theplasma-excitation gas such as Ar or Kr, there is caused an excitation ofactive species such as atomic state oxygen O* or hydrogen nitrideradicals NH* in the process space 11B by the high-density plasma, and itbecomes possible to conduct oxidation processing, nitridation processingor oxynitridation processing on the surface of the substrate 12.

Further, there is proposed a substrate processing apparatus 10A shown inFIG. 3 having a construction similar to the substrate processingapparatus 10 of FIG. 2 except that there is provided a lower showerplate 31 at the lower side of the shower plate 14. The lower showerplate 31 is provided with a process gas passage 31A communicating with aprocess gas inlet port 11 r formed at the surface of the processingvessel 1 and a large number of process gas inlet nozzle openings 31B areformed in communication with the process gas passage 31A. Further, thelower shower plate 31 is provided with large apertures for passing theprocess gas radicals formed in the space 11B.

Thus, in the substrate processing apparatus 10A of FIG. 3, there isdefined another process space 11C underneath the lower shower plate 31.By forming the lower shower plate 31 by a conductive material such as astainless steel having a passivation surface by aluminum oxide (Al₂O₃)in such an apparatus, it becomes possible to block the penetration ofmicrowave to the process space 11C. Thereby, the excitation of plasma islimited in the process space 11B right underneath the upper shower plate14, and the radicals Kr* of Kr or Ar* of Ar penetrate into the processspace 11C through the large apertures formed in the shower plate 31after excitation in the space 11B. The radicals Kr* or Ar* thuspenetrated into the process space 11C cause activation of the processgas released from the nozzle apertures 31B, and the processing of thesubstrate 12 is achieved by the process gas radicals thus activated.

In the substrate processing apparatus 10A of FIG. 3, it should be notedthat the microwave is expelled from the process space 11C by forming thelower shower plate 31 by a conductive material, and the damaging of thesubstrate by microwave is avoided.

In the substrate processing apparatus 10A of FIG. 3, it is also possibleto conduct a plasma CVD process by introducing a CVD source gas from thelower shower plate 31. Further, it is possible to conduct a dry etchingprocess by introducing a dry etching gas from the lower shower plate 31and applying a high-frequency bias to the stage 13.

Thus, in the substrate processing apparatus of FIG. 2 of FIG. 3, Krradicals (Kr*) of intermediate excitation state having an energy ofabout 10 eV are excited at the time of conducting an oxidationprocessing, by introducing a Kr gas and an oxygen gas into the processspace 11B. The Kr radicals thus excited cause efficient excitation ofatomic state oxygen O* according to the reactionO₂→O*+O*,while the atomic state oxygen O* thus excited cause the desiredoxidation of the surface of the substrate 12.

In the case of conducting a nitridation processing of the substrate 12,a Kr gas and an ammonia gas, or a Kr gas and a nitrogen gas and ahydrogen gas are introduced. In this case, the excited Kr radicals (Kr*)or Ar radicals (Ar*) cause the excitation of hydrogen nitride radicalsNH* according to the reactionNH₃→NH*+2H*+e ⁻,orN₂+H₂→NH*+NH*,wherein the hydrogen nitride radicals thus excited cause the desirednitridation processing of the substrate of the surface 12.

Meanwhile, there are cases in which it is preferable to use atomic statenitrogen (N*), free from hydrogen and having a strong nitriding power,at the time of the nitridation processing of the substrate. The atomicstate nitrogen N* are formed according to the reactionN₂→N*+N*,wherein it should be noted that such a reaction requires the energy of23-25 eV. This means that it is not possible to excite the atomic statenitrogen N* according to the foregoing reaction, as long as Kr or Arplasma is used. As noted previously, the energy of the Kr radicals or Arradicals obtained by the Kr or Ar plasma is merely in the order of 10eV.

Thus, even when there is made an attempt to supply a nitrogen gas in thesubstrate processing apparatus of FIG. 2 or FIG. 3 in place of the Krgas or the Ar gas, merely the reactionN₂→N₂ ⁺ +e ⁻,is obtained, and there is caused no desired atomic state oxygen N*.

FIG. 4 shows the relationship between the state density of the Kr plasmaand the excitation energy of the atomic state nitrogen N*, hydrogennitride radicals NH* and nitrogen atoms N₂ ⁺.

Referring to FIG. 4, it can be seen that the state density of the Krplasma is large at the low energy side, while the state density shows arapid decrease with increase of the energy. Such a plasma cannot achieveefficient excitation of the desired nitrogen radicals.

DISCLOSURE OF THE INVENTION

Accordingly, it is a general object of the present invention to providea novel and useful substrate processing apparatus wherein the foregoingproblems are eliminated.

Another and more specific object of the present invention is to providea substrate processing method and apparatus capable of forming nitrogenradicals N* efficiently.

Another object of the present invention is to provide a method ofprocessing a substrate by using a substrate processing apparatus whichhas such a construction that a process space, in which a substrate to beprocessed is contained, is separated from a plasma formation space, inwhich the substrate to be processed is not contained, by a controlelectrode in a processing vessel, characterized by the steps of:

supplying a gas containing He and N₂ to said processing vessel;

forming plasma in said plasma formation space under a condition suchthat there is caused excitation of atomic state nitrogen N* in saidplasma; and

nitriding a surface of the substrate to be processed by said atomicstate nitrogen N* in said process space.

Another object of the present invention is. to provide a substrateprocessing apparatus, comprising:

a processing vessel defined by an outer wall and having a stage forholding a substrate to be processed thereon;

an evacuation system coupled to said processing vessel;

a plasma gas supplying part supplying a plasma excitation gas and aprocess gas into said processing vessel;

a microwave window provided on said processing vessel so as to face saidsubstrate to be processed; and

a control electrode provided between said substrate to be processed onsaid stage and said plasma gas supplying part so as to face saidsubstrate to be processed and separating a plasma excitation spacecontaining said microwave window and a process space containing saidsubstrate to be processed,

said control electrode comprising a conductive member having a pluralityof apertures for passing plasma formed in said processing vesseltherethrough, and

a surface of said control electrode being covered by any of aluminumoxide or electrically conductive nitride.

Another object of the present invention is to provide a substrateprocessing apparatus, characterized by:

a processing vessel defined by a wall of quartz glass and having a stagefor holding a substrate to be processed;

an evacuation system coupled to said processing vessel;

a plasma gas supplying part supplying a plasma excitation gas and aprocess gas to said processing vessel;

a control electrode provided so as to face said substrate to beprocessed on said stage and dividing an interior of said processingvessel into a process space containing said substrate to be processedand a plasma excitation space; and

an induction coil provided outside said quartz glass wall incorrespondence to said plasma excitation space,

said control electrode comprising a conductive member having a pluralityof apertures passing therethrough plasma formed in said processingvessel, and

a surface of said control electrode being covered with any of aluminumoxide or electrically conductive nitride.

According to the present invention, it becomes possible to form plasmahaving the energy sufficient for causing excitation of atomic statenitrogen N* in the substrate processing apparatus by using He for theplasma excitation gas, and it becomes possible to conduct an efficientnitridation of the substrate by using the atomic state nitrogen N* thusexcited. By separating the plasma excitation space in which thehigh-density plasma is excited from the process space in which thesubstrate is included by means of the control electrode, it becomespossible to reduce the plasma energy in the process space to the levelsuitable for substrate processing. Further, it becomes possible to trapthe positive ions formed in the plasma excitation space. In the case ofapplying the present invention to the substrate processing apparatusthat uses microwave-excited plasma, it becomes possible to avoidexcessive increase of the plasma energy by conducting the plasmaexcitation by using a microwave having the frequency of about 28 GHz ormore.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a diagram showing the construction of a conventional inductioncoupled plasma processing apparatus;

FIG. 2 is a diagram showing the construction of a previously proposedmicrowave substrate processing apparatus;

FIG. 3 is a diagram showing the construction of another previouslyproposed microwave substrate processing apparatus;

FIG. 4 is a diagram explaining the characteristics of plasma excitationin the microwave substrate processing apparatus of FIG. 2 or FIG. 3;

FIG. 5 is a diagram showing the construction of a microwave substrateprocessing apparatus according to a first embodiment of the presentinvention;

FIG. 6 is a diagram showing a part of the microwave substrate processingapparatus of FIG. 5;

FIG. 7 is a diagram showing the characteristics of plasma excitation inthe microwave substrate processing apparatus of FIG. 5;

FIG. 8 is a diagram showing a modification of the microwave plasmaprocessing apparatus of FIG. 5;

FIG. 9 is a diagram showing the construction of a microwave plasmaprocessing apparatus according to a second embodiment of the presentinvention; and

FIG. 10 is a diagram showing the construction of an induction coupledplasma processing apparatus according to a third embodiment of thepresent invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[First Embodiment]

FIG. 5 shows the construction of a substrate processing apparatus 100according to a first embodiment of the present invention. In FIG. 5,those parts corresponding to the parts described previously aredesignated by the same reference numerals and the description thereofwill be omitted.

Referring to FIG. 5, the shower plate 14 is mounted on the processingvessel 11 via a seal 11 s, and the cover plate 15 is mounted on theshower plate 14 via a seal 11 t. Further, the radial line slot antenna20 is mounted on the processing vessel 11 via a seal 11 u.

Further, in the substrate processing apparatus 100 of FIG. 5, theinterface between the emission plate 16 and the cover plate 15 isevacuated via a ring-shaped groove 11 g formed at the top part of theprocessing vessel 11 in the region where the processing vessel makes anengagement with the emission plate and further via an evacuation port11G communicating with the ring-shaped groove 11 g. After evacuation, aHe gas is introduced into the foregoing interface with a pressure ofabout 0.8 atmospheres as a thermal conducting medium. The He gas thusintroduced is confined therein by closing the valve 11V.

In the substrate processing apparatus 100 of FIG. 5, it should be notedthat the lower shower plate 31 used in the substrate processingapparatus 10A of FIG. 3 is removed and a control electrode 131 of aconductive member is formed, wherein the control electrode 31 has alattice shape as represented in FIG. 6 and is formed so as to separatethe plasma excitation space 11B and the process space 11C.

Referring to FIG. 6, the lattice-shaped control electrode 131 is formedwith large number of apertures 132 having a size set such that thereoccurs free passage of the radicals excited in the plasma excitationspate 11B, and thus, the plasma excited in the plasma excitation space11B cause diffusion freely into the process space 11C through thecontrol electrode 131.

In the construction of FIG. 5, it should be noted that thelattice-shaped control electrode 131 is grounded, and thus, themicrowave introduced into the plasma excitation space 11B from theradial line slot antenna 11B is reflected by the lattice shaped controlelectrode 131, and there is caused no invasion of the microwave into theprocess space 11C. Thus, the problem of the microwave causing damages inthe substrate 12 is not caused in the substrate processing apparatus 100of FIG. 5.

It should be noted that the lattice-shaped control electrode 131 can beformed by W, Ti, or the like, wherein it is possible to increase theresistance against plasma irradiation by forming a layer 131 a of aconductive nitride such as WN or TiN on the surface thereof. Further, itis possible to form such a lattice-shaped control electrode 131 by usinga quartz glass and provide the conductive nitride layer 131 a on thesurface thereof. Further, in the substrate processing apparatus 100, itshould be noted that the sidewall surface of the processing vessel 11 iscovered by a quartz liner 11D for the part corresponding to the plasmaexcitation space 11B

In the substrate processing apparatus 100 of FIG. 5, a He gas and an N₂gas are introduced to the process gas inlet port 11 p, and a microwaveof about 28 GHz is supplied to the radial line slot antenna. Typically,the process pressure in the processing vessel 11 is set to the range of66.5-266 Pa (0.5-2 Torr), and nitridation processing or oxynitridationprocessing of the substrate 12 is conducted in the temperature range of200-500° C.

FIG. 7 shows the state density of the plasma excited in the substrateprocessing apparatus 100 of FIG. 5 for the case He is used for theplasma gas.

Referring to FIG. 7, it should be noted that the use of He having acharacteristically small collision cross-section for the plasma gascauses significant acceleration in the excited He radicals He* with themicrowave electric field, and as a result, there is caused significantincrease of plasma energy to the level suitable for excitation of theatomic state nitrogen N*. On the other hand, it can be seen that theefficiency of excitation of the hydrogen nitride radicals NH* ornitrogen ions N₂ ⁺, which are excited efficiently in the case Kr is usedfor the plasma gas, is reduced significantly.

Thus, in the present invention, efficient excitation of the atomic statenitrogen N* is achieved in the substrate processing apparatus 100 at thehigh plasma energy of 23-25 eV by using He for the plasma gas. In orderto avoid excessive increase of the electron temperature in the plasma,the present invention uses a microwave source 22 that produce amicrowave of the frequency higher than the previously proposedfrequency, such as about 28 GHz or more, for driving the radial lineslot antenna 20. Thereby, it is possible to select the frequency of themicrowave source from the frequencies such as about 2.4 GHz or about 8.3GHz. Further, by separating the plasma excitation space 1lB and theprocess space 11C by the control electrode 131, it is possible to reducethe electron temperature and the plasma energy to a level suitable forsubstrate processing.

Particularly, it should be noted that the control electrode is protectedeffectively from the high-energy plasma by forming a conductive nitridesuch as an Al₂O₃ passivation film on the surface of the controlelectrode 131 as explained already. Further, the problem of sputteringof the inner wall of the processing vessel by the high-energy plasma andthe associated problem of contamination of the substrate are avoided bycovering the inner wall of the processing vessel 11 by a quartz liner11D for the part corresponding to the plasma excitation region 11B.

FIG. 8 shows the construction of a substrate processing apparatus 100Aaccording to a modification of the present embodiment.

Referring to FIG. 8, it becomes possible in the substrate processingapparatus 100A to capture the nitrogen ions N₂ ⁺ excited in the plasmaexcitation space 11B with the positive electric charge, by controllingthe potential of the control electrode 31 to a suitable negativepotential value. Thereby, penetration of the nitrogen ions N₂ ⁺ into theprocess space 11C is avoided.

In the substrate processing apparatus 100 or 100A of the presentembodiment, it is possible to conduct an oxynitridation processing ofthe substrate 12 by supplying a He gas, an N₂ gas and an O₂ gas to theplasma gas supply port 11 p.

[Second Embodiment]

FIG. 9 shows the construction of a substrate processing apparatus 200according to a second embodiment of the present invention. In FIG. 9,those parts corresponding to the parts described previously aredesignated by the same reference numerals and the description thereofwill be omitted.

Referring to FIG. 9, it should be noted that the shower plate 14 isremoved in the present embodiment, and in place of this, there areprovided a plurality of process gas inlet ports lip on the processingvessel 11 such that the process gas inlet ports 11P are disposed with asymmetric relationship with respect to the substrate 12. As a result,therefore, the cover plate 15 constituting the dielectric window isexposed at the top part of the plasma excitation space 11B. Further, thesidewall surface of the processing vessel is covered by the quartz liner11D for the part corresponding to the plasma excitation space 11Bsimilarly to the previous embodiment.

According to the present embodiment, the construction of the substrateprocessing apparatus 11 is simplified, and it becomes possible toconduct the nitridation processing of the substrate 12 efficiently withlow cost by using the atomic state nitrogen N*, by supplying a He gasand an N₂ gas to the plasma gas supplying port lip and by supplying themicrowave of about 28 GHz to the radial line slot antenna 20. Further,it is possible to conduct an oxynitridation processing by supplying a Hegas, an N₂ gas and an O₂ gas to the plasma gas supplying port 11 p.

[Third Embodiment]

FIG. 10 shows the construction of a substrate processing apparatus 300according to a third embodiment of the present invention. In FIG. 10,those parts corresponding to the parts described previously aredesignated by the same reference numerals and the description thereofwill be omitted.

Referring to FIG. 10, the substrate processing apparatus 300 has aconstruction similar to the substrate processing apparatus 1 explainedbefore with reference to FIG. 1, except that a control electrode 6similar to the control electrode 31 is provided in the quartz vessel 2,and the space inside the quartz vessel 2 is divided by the controlelectrode 6 into a plasma excitation space 2B1 in which the high-densityplasma 2D is excited and a process space 2B2 that includes the substrate4 to be processed.

In the present embodiment, a He gas and an N₂ gas are introduced intothe plasma excitation space 2B1 via the process gas supply line 2C, andthere is formed high-density plasma 2D having a high electrontemperature and plasma energy sufficient for exciting atomic statenitrogen N* in the plasma excitation space 2B1.

The atomic state nitrogen N* thus formed cause diffusion into theprocess space 2C through the control electrode 6, and the surface of thesubstrate 4 undergoes nitridation. In such a construction, it should benoted that the plasma has a very high electron temperature and energy inthe plasma excitation space 2B1, while the electron temperature and theenergy of the plasma are reduced to the level suitable for processingthe substrate 4 in the process space 2B2.

In the present embodiment, too, it becomes possible to remove the lowenergy positive ions such as N₂ ⁺ formed in the plasma excitation space2B1 from the process space 2B2 by trapping the same, by controlling thepotential of the control electrode 6 by the voltage source 6A. Further,it becomes possible to control the state of the high-density plasma 2Din the plasma excitation space 2B1 by controlling the potential of thecontrol electrode 6.

In the substrate processing apparatus 200 of the present embodiment, itis also possible to conduct an oxynitridation processing of thesubstrate 4 in the process space 2B₂ by introducing a He gas and an N₂gas and an O₂ gas from the process gas supply line 2C.

Further, the present invention is not limited to the specific preferredembodiments described heretofore, but various variations andmodifications may be made without departing from the scope of theinvention recited in the claims.

INDUSTRIAL APPLICABILITY

According to the present invention, it becomes possible to form plasmahaving the energy sufficient for causing excitation of atomic statenitrogen N* in the substrate processing apparatus by using He for theplasma excitation gas, and it becomes possible to conduct an efficientnitridation of the substrate by using the atomic state nitrogen N* thusexcited. By separating the plasma excitation space in which thehigh-density plasma is excited from the process space in which thesubstrate is included by means of the control electrode, it becomespossible to reduce the plasma energy in the process space to the levelsuitable for substrate processing. Further, it becomes possible to trapthe positive ions formed in the plasma excitation space. In the case ofapplying the present invention to the substrate processing apparatusthat uses microwave-excited plasma, it becomes possible to avoidexcessive increase of the plasma energy by conducting the plasmaexcitation by using a microwave having the frequency of about 28 GHz ormore.

1. A method of processing a substrate by using a substrate processingapparatus which has such a construction that a process space, in which asubstrate to be processed is contained, is separated from plasmaformation space, in which the substrate to be processed is notcontained, by a control electrode in a processing vessel, characterizedby the steps of: supplying a gas containing He and N₂ to said processingvessel; forming plasma in said plasma formation space under a conditionsuch that there is caused excitation of atomic state nitrogen N* in saidplasma; and nitriding a surface of the substrate to be processed by saidatomic state nitrogen N* in said process space.
 2. The substrateprocessing method as claimed in claim 1, characterized in that said stepof forming plasma is conducted such that an intermediate excitationstate of the energy of 23 to 25 eV is realized.
 3. The substrateprocessing method as claimed in claim 1, characterized in that said stepof forming plasma comprises the step of supplying a microwave to saidplasma formation space.
 4. The substrate processing method as claimed inclaim 3, characterized in that said step of supplying microwave isconducted by driving a radial line slot antenna.
 5. The substrateprocessing method as claimed in claim 1, characterized in that said stepof forming plasma comprises the step of forming an induction magneticfield in said plasma formation space.
 6. The substrate processing methodas claimed in claim 5, characterized in that said step of forming aninduction magnetic field comprises the step of driving an induction coilwound around said processing vessel by a high frequency electric power.7. The substrate processing method as claimed in claim 1, characterizedin the said control electrode is grounded during said step of excitingplasma.
 8. The substrate processing method as claimed in claim 1,characterized in that a negative potential is supplied to said controlelectrode in said step of forming plasma.
 9. The substrate processingmethod as claimed in claim 1, wherein said gas supplied to saidprocessing vessel further contains O₂.
 10. A substrate processingapparatus, comprising: a processing vessel defined by an outer wall andhaving a stage for holding a substrate to be processed thereon; anevacuation system coupled to said processing vessel; a plasma gassupplying part supplying a plasma excitation gas and a process gas intosaid processing vessel; a microwave window provided on said processingvessel so as to face said substrate to be processed; and a controlelectrode provided between said substrate to be processed on said stageand said plasma gas supplying part so as to face said substrate to beprocesed, and separating a plasma excitation space containing saidmicrowave window and a process space containing said substrate to beprocessed, said control electrode comprising a conductive member havinga plurality of apertures for passing plasma formed in said processingvessel therethrough, and a surface of said control electrode beingcovered by any of aluminum oxide or electrically conductive nitride. 11.The substrate processing apparatus as claimed in claim 10, characterizedin that said control electrode has a lattice-shaped form and isgrounded.
 12. The substrate processing apparatus as claimed in claim 10,characterized in that said control electro has a form of a lattice-likeshape and said substrate processing apparatus comprises a negativevoltage source connected to said control electrode.
 13. The substrateprocessing apparatus as claimed in claim 10, characterized in that aninner wall of said processing vessel is covered with an insulation filmin said plasma excitation space.
 14. The substrate processing apparatusas claimed in claim 10, characterized by further comprising a microwaveantenna coupled to said microwave window at an outer side of saidprocessing vessel.
 15. A substrate processing apparatus, characterizedby: a processing vessel defined by a wall of quartz glass and having astage for holding a substrate to be processed; an evacuation systemcoupled to said processing vessel; a plasma gas supplying part supplyinga plasma excitation gas and a process gas to said processing vessel; acontrol electrode provided so as to face said substrate to be processedon said stage and dividing an interior of said processing vessel into aprocess space containing said substrate to be processed and a plasmaexcitation space; and an induction coil provided outside said quartzglass wall in correspondence to said plasma excitation space, saidcontrol electrode comprising a conductive member having a plurality ofapertures passing therethrough plasma formed in said processing vessel,and a surface of said control electrode being covered with any ofaluminum oxide or electrically conductive nitride.
 16. The substrateprocessing apparatus as claimed in claim 15, characterized in that saidquartz glass wall defines a dome-like space.
 17. The substrateprocessing apparatus as claimed in claim 15, characterized in that saidcontrol electrode is grounded.
 18. The substrate processing apparatus asclaimed in claim 15, characterized in that said control gate isconnected to a negative voltage source.